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GN/MAE155B10 Orbital Perturbation Effects: Regression of Nodes Regression of Nodes: Equatorial bulge causes component of gravity vector acting on SC to be slightly out of orbit plane This out of orbit plane component causes a slight precession of the orbit plane. The resulting orbital rotation is called regression of nodes and is approximated using the dominant gravity harmonics term, J2

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GN/MAE155B12 Orbital Perturbation: Rotation of Apsides  Rotation of apsides caused by earth oblateness is similar to regression of nodes. The phenomenon is caused by a higher acceleration near the equator and a resulting overshoot at periapsis. This only occurs in elliptical orbits. The rate of rotation is given by:

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GN/MAE155B15 Spacecraft Horizon SC horizon forms a circle on the spherical surface of the central body, within circle: –SC can be seen from central body –Line of sight communication can be established –SC can observe the central body